Over the past several years, the Fibroblast Growth Factor (FGF) and Sprouty signalling pathways have been shown to play a key role in development of dental morphology. Yet despite the extensive investigation of this pathway in tooth development, a critical question has gone unanswered: what are the genetic mechanisms involved in patterning the different elements of the occlusal surface (cusps and crests)? Using 24 rodent species, we have begun to describe 66 unique dental morphologic characters for each species. In addition, we have identified 26 coding and non-coding regions of Fgf3,4,8,9, and 10, conserved among all 24 species. I hypothesize that the interspecific variation of murid dental morphology is governed by the variation of the regulatory genetic code, which works through the orchestration of the variable spatio-temporal expression of the signaling molecules involved in embryonic development. I propose to use the mouse model as well as several in-vitro mouse tooth models to investigate the role of the spatio-temporal variation in expression of FGF and Sprouty signalling pathway members in variation of tooth morphology. The overarching goal of this project is to further investigate the role of genetic regulatory machinery variation as a mechanism of creation of new dental phenotypes. Since such mechanisms may not only yield character states which promote a species' fitness, but sometimes greatly hinder it, as the case with defective phenotypes, understanding the precise genetic mechanisms which drive evolution can further our understanding of the origins of developmental anomalies.